The long-range goal of our laboratory is to determine how oligodendrocyte development, myelin synthesis and maintenance, and remyelination are regulated at the molecular, cellular and organismal level. In this application we propose to test the hypothesis that cyclic AMP (cAMP) and insulin-like growth factor I (IGF-I), which we have previously identified as key regulators of oligodendrocyte development and function, regulate myelin synthesis by promoting one or more of the following steps: the switching on of genes for myelin components; transcription of selected genes; accumulation of the relevant mRNAs; and synthesis or stabilization of myelin components. To enable an efficient and straightforward experimental approach to these questions, we propose to develop a novel in vitro system of immortal oligodendrocytes and oligodendrocyte progenitors, produced by transfection of cells with an oncogene whose expression can be turned on by the investigator to achieve unlimited proliferation of clonally pure cells, and then turned off to allow expression only of endogenous cellular genes. (We will also produce clones of mouse oligodendrocytes and human oligodendrocytes for use as experimental material in other studies.) We will expose the cells in vitro to IGF-I or cAMP analogs and apply biochemical, immunochemical, cell biological and molecular genetic techniques to determine (1) at what step(s) the inducers act to promote myelin-associated functions, and (2) how the induction occurs. From these investigations, we expect to learn the molecular and biochemical basis for the regulation of oligodendrocyte development and the synthesis of myelin components by two potent regulatory agents. The results should give valuable insight into how myelination is controlled, and will be useful in attempting to understand the defects that occur in disorders of myelin. Moreover, the results may ultimately lead to the development of approaches to promoting remyelination in MS or other disorders.